Nicholas P Skinner

Characterising the effective intensity of multiple-pulse flashing signal lights

Flashing lights used in aviation signal applications can be characterised by the luminous intensity of a steady-burning signal light with the same visual effectiveness. Different formulae exist for calculating the effective intensity of flashing signal lights that use multiple brief pulses of light within each flash. The results of a laboratory study conducted to test these calculation methods revealed that a formulation based on the Blondel–Rey–Douglas effective intensity method was more predictive of judgments of overall visibility than a different formulation published in recent aviation authority guidance. A follow-up experiment yielded confirmation of these findings. Different aspects of visibility resulted in very different judgments, and the limitations of the effective intensity concept to characterise the visibility of a flashing light are also discussed.

Real-World Measurement of Headlamp Illumination

This paper discusses a study that collected data regarding headlight visibility or glare. It describes a system intended to be mounted in a parking facility, road curve, or intersection, that is capable of collecting this data. The system is self-governing and it can gather information from many vehicles during a data collection period. The system includes a digital camera, a range finder, light sensors, and an illuminance meter. It measures headlight position (mounting height), vertical headlight illumination, and angular location of the eyes of a driver in an oncoming vehicle. It is possible to determine headlight aim distribution from the data gathered. The data also provide an estimation of the distribution of levels of light that reach the eyes of drivers in oncoming vehicles.

Conspicuity of flashes of light: interactions between intensity and duration

Flashing lights are used in visual signaling applications to provide attention-getting properties. While the effective intensity concept for quantifying the visual effectiveness of flashing signal lights relative to steady-burning lights generally ranks signals properly with respect to conspicuity, brightness, and overall visibility, these responses differ substantially in terms of the absolute intensity needed to achieve each response. To better understand the role of flashing light characteristics (intensity, duration and flash energy) on visual responses, a laboratory experiment was conducted to assess the relative brightness and apparent speed of onset of simultaneously presented, suprathreshold flashes of white light under dark viewing conditions. Judgments of brightness were mainly dependent upon the flash energy. Judgments of apparent speed were unrelated to flash duration for short flashes (duration ⩽ 25 ms) but dependent upon flash duration for longer durations (25 ms ⩽ duration ⩽ 125 ms). The results can provide some guidance regarding flashing light characteristics to optimize different visual responses.

Visual Recovery and Discomfort Following Exposure to Oncoming Headlamps

The effects of various temporal and photometric characteristics of profiles of oncoming illumination on subjects discomfort and on visual recovery were examined in field experiments. Older subjects took a longer time to recover, but there were no differences of rated discomfort between the age groups. Rated discomfort was correlated with peak illumination of each profile, and target detection time was correlated with dosage.

Evaluation of Light-Emitting Diode Warning Beacons for Maintenance Vehicles

Rotating warning beacons containing filament light sources have long been used on highway maintenance vehicles to indicate the presence of the vehicle to other drivers. Flashing warning beacons containing light-emitting diodes (LEDs) are beginning to be used in place of rotating warning beacons, in part because they use considerably less power. To help ensure that LED warning beacons will provide a comparable warning signal to drivers who approach vehicles outfitted with them, the photometric and temporal characteristics of LED warning beacons were measured and compared with data on human response time. In addition, several LED warning beacons were compared with a conventional incandescent rotating warning beacon in regard to the distance at which observers could detect that a vehicle had moved closer. Pairs of LED warning beacons provided closure detection distances that were equivalent to pairs of conventional rotating beacons. Although single LED warning light configurations were not tested, the pairs of LED beacons that were tested reliably outperformed a single conventional beacon configuration for both energy use and closure detection distance. Results suggested that LED warning beacons provide comparable visual information to other drivers and use substantially less power than conventional rotating beacons do.

Toward the development of standards for yellow flashing lights used in work zones

Flashing yellow warning lights are important for worker and driver safety in work zones. Current standards for these lights do not address whether and how they should be coordinated to provide directional information to drivers navigating through work zones. A field study was conducted to assess driver responses to warning lights. The luminous intensities and flash patterns of warning lights along a simulated work zone were varied during daytime and nighttime. During the daytime, driver responses were relatively insensitive to warning light characteristics, although drivers preferred sequential and synchronised flash patterns over random, uncoordinated flashing. At nighttime, the combination of a temporal peak luminous intensity of 25 cd and a sequential flash pattern was optimal for providing directional information. A single initial warning light having a higher luminous intensity may help drivers detect the work zone without creating unacceptable visual discomfort.

High visibility reflective sign sheeting materials: field and computational evaluations of visual performance

Highway signs provide important information to drivers to assist in navigation, to identify potentially hazardous roadway locations, and to remind drivers of safe operating practices. Ensuring that signs have sufficient visibility to the driving public is a key undertaking by transportation agencies. In order to assist in evaluating and comparing different materials for photometric and visual performance, the present study was undertaken to assess the utility of specifying sign sheeting performance in terms of visual performance. As part of this effort, a practical methodology for conducting field measurements of sign luminance along roadways was developed. In addition to describing the methods for an approach to visual performance based specifications, a spreadsheet tool for calculating minimum sign luminance and visibility from different sign sheeting materials was also developed. First published online 20 October 2016

Assessment of Adaptive Driving Beam Photometric Performance

This paper focuses on the safety benefits of adaptive driving beam headlights. The photometric performance of the headlights is tested in the field using simulated headlight and tail light conditions. The test results are summarized and recommendations for standardized measurement conditions for reliability are also provided.

Work Zone Lighting and Visual Performance: Analysis and Demonstration

In part because of the potential for high levels of glare from work zone illumination, recommendations for light levels from work zone illumination systems are substantially higher than for levels used along roadways in non–work zone locations. In a two-part study, requirements for work zone illumination light levels were assessed. First, levels for workers varying in age from 20 to 60 years were evaluated with the relative visual performance model, with and without the presence of visibility-reducing glare. Except for the smallest, lowest-contrast tasks performed by the older workers, an illuminance of 10 lx resulted in visibility well above the threshold even in the presence of glare, and an illuminance of 30 lx resulted in suprathreshold visibility for these conditions as well. The results of these computational analyses were largely confirmed in a full-scale, outdoor field demonstration attended by transportation agency engineers and highway contractors. Together, the findings suggest that when lighting systems provide sufficient glare control, light levels do not always need to be especially high to ensure adequate visibility for workers.

Effect of Dynamic Lighting Conditions on Visual Detection

Various lighting configurations were created with different levels of foreground uniformity and illumination in order to investigate the role of foreground uniformity and illumination level on driver visual performance and preference. Results of the experiment indicate that drivers prefer high illumination levels in the foreground, though they do not have to be uniform. However, visual detection of objects further down the road was slightly (though not at a significant level) worse when foreground illumination levels were higher.